Iran hacked unclassified Navy computers within the last few weeks, according to anonymous U.S. officials.

The officials say the attacks, which breached an unclassified computer network, were done by hackers working directly for the Iranian government or for a group acting with governmental approval. They said that they do not believe that any data of significant importance was stolen. Iranian cyber-warfare capabilities were previously thought to be negligible, and Iranian attacks typically focused on American banks and energy companies.

Secretary of Defense Chuck Hagel and chairman of the Joint Chiefs of Staff General Martin Dempsey have both been briefed on the intrusions, as has Congress.

News of the attacks broke shortly after President Obama revealed that he had spoken by phone with Iranian president Hassan Rouhani, the first communications between the American and Iranian heads of state since 1979.